Hard drive size not correct.

Hello all, my problem is this; I've installed a 15GB Hitachi laptop
drive into a really old laptop (P133) the bios doesn't support this
size, and I can't get an update for it (IPC radiance-its that old!)so
I got hold of a copy of disk manager (ver.6 I think) and used this to
overlay the HD. Using Fdisk I have 2 partitions, 1st one is
8GB(primary) and the second is 6GB(logical drive on extended)
(rounding down). Installing win98se onto the HD, I find that after
installation win98 reports the boot partition (C: drive) as 3.89GB in
my computer, but the 2nd partition D:,as 6GB(which is ok). How is this
possible? Is it win98se somehow getting the wrong drive info from the
overlay program? What has happened to the other 4GB on drive C: ???
Please help, I have tried to reinstall a few times but still get the
same problem , my only other option is to fdisk and make c: 4GB and a
big 10GB 2nd partition. But again I think the 2nd partition will not
be properly recognized.